Re: [PATCH V5 16/16] block: ublk_drv: apply io_uring FUSED_CMD for supporting zero copy

[Ziyang Zhang]

On 2023/3/28 23:09, Ming Lei wrote:
> Apply io_uring fused command for supporting zero copy:
> 

[...]

>  
> @@ -1374,7 +1533,12 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
>  	if (!ubq || ub_cmd->q_id != ubq->q_id)
>  		goto out;
>  
> -	if (ubq->ubq_daemon && ubq->ubq_daemon != current)
> +	/*
> +	 * The fused command reads the io buffer data structure only, so it
> +	 * is fine to be issued from other context.
> +	 */
> +	if ((ubq->ubq_daemon && ubq->ubq_daemon != current) &&
> +			(cmd_op != UBLK_IO_FUSED_SUBMIT_IO))
>  		goto out;
>  

Hi Ming,

What is your use case that fused io_uring cmd is issued from another thread?
I think it is good practice to operate one io_uring instance in one thread
only.

Regards,
Zhang